1. Field of the Invention
This invention relates to an electromagnetic relay, and more particularly, to an electromagnetic relay which includes a member for indicating the operation of the relay.
2. Related Art
A conventional relay with an operation indicating member includes a housing formed by a case and a base. The case has a window through which operation of the relay can be seen. An electromagnet fixed to a yoke is attached to the base through the yoke using a rivet.
A movable iron member is pivotally mounted on the tip of the yoke so that the iron member can make contact with an iron core of the electromagnet. The movable iron member includes an electrical insulator support to which a movable member is fixed. The movable member carries a movable contact on the tip thereof. A terminal fixed to the base includes a stationary contact, and another terminal fixed to the base also includes a stationary contact. The two stationary contacts are horizontally opposite to each other. The movable member is arranged so that the movable contact can be disposed between the two stationary contacts. The movable contact makes contact with one of the stationary contacts when the electromagnet is in an inactivated condition.
A plate for indicating operation of the relay (operation indicating plate) is vertically provided between the insulator support and the case. A fulcrum at the lower portion of the plate rests on the base and is tightly sandwiched between a first of the terminals and the case. A locking projection horizontally fixed on the shank of the plate engages the insulator support. The operation indicating plate is arranged so that the tip thereof cannot be seen through the window of the case when the electromagnet is in the inactivated condition.
When the electromagnet is energized, the movable iron member is attracted to the iron core of the electromagnet. The movable contact accordingly breaks contact with the first of the stationary contacts, and comes into contact with the other. At the same time, the operation indicating plate is biased to a predetermined position, and the tip of the indicating plate thus can be seen through the window. Consequently, the operation of the relay can be checked.
However, since the indicating plate is placed near the contacts, it is easily heated and deformed by the heat of the arc discharge between the movable contact and the stationary contacts. In addition, current flowing through the terminals causes the terminal to be heated. The heat of the terminals also causes the deformation of the fulcrum. The deformed fulcrum renders the normal movement of the indicating plate difficult, and the indicating plate thus fails to move to the predetermined position. The tip of the indicating plate therefore cannot be seen through the window of the case. Consequently, the operation of the relay cannot be checked.
In the foregoing relay, the rivet is horizontally moved to adjust the contact pressure. However, moving the rivet to an undesired position results in a malfunction of the indicating plate or in the indicating plate being only loosely fixed within the device.